Heat transfer through a catheter tip

ABSTRACT

Described embodiments include a catheter tip that includes an outer layer of a thermally-conducting metal; an inner layer of a thermally-conducting metal; a polymer layer between the inner and outer layer; and a plurality of thermal bridges selectively positioned between the inner and outer layers and through the polymer layer thereby significantly increasing the heat transfer of the catheter tip through the polymer layer. Other embodiments are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of prior filed U.S. patentapplication No. 15/990,532 filed on May 25, 2018.

FIELD

The present disclosure is related to ablation catheters and the usethereof in ablation procedures.

BACKGROUND

In some ablation procedures, an electrode disposed at the catheter tipof an ablation catheter is brought into contact with tissue, andradiofrequency (RF) energy is then passed from the electrode into thetissue. The RF energy raises the temperature of the tissue, thuscreating lesions in the tissue.

US Patent Application Publication 2018/0110562, whose disclosure isincorporated herein by reference, describes a catheter that includes aninsertion tube, a flexible substrate, and one or more electricaldevices. The insertion tube is configured for insertion into a patientbody. The flexible substrate is configured to wrap around a distal endof the insertion tube and includes electrical interconnections. Theelectrical devices are coupled to the flexible substrate and areconnected to the electrical interconnections.

SUMMARY

There is provided, in accordance with some embodiments of the presentdisclosure, an electrophysiology catheter tip that includes a flexiblethermally-insulating substrate that includes an inner surface and anouter surface and is shaped to define (i) multiple narrower channelspassing between the inner surface and the outer surface, and (ii) one ormore wider channels passing between the inner surface and the outersurface. The tip further includes an outer layer of an electrically andthermally-conducting metal covering at least part of the outer surface,an inner layer of the electrically and thermally-conducting metalcovering at least part of the inner surface, a plating layer of theelectrically and thermally-conducting metal that plates the widerchannels such as to connect the outer layer to the inner layer, andrespective columns of the thermally-conducting metal that fill thenarrower channels such as to connect the outer layer to the inner layer.

In some embodiments, the substrate is shaped to define at least 1,000narrower channels.

In some embodiments, a total area of respective outer openings of thenarrower channels is at least 10% of an area of the outer surface.

In some embodiments, the electrically and thermally-conducting metalincludes gold.

In some embodiments, the tip further includes:

at least one constantan trace disposed on the inner surface andelectrically isolated from the inner layer; and

at least one gold trace disposed on the inner surface, electricallyisolated from the inner layer, and covering the constantan trace at athermocouple junction.

In some embodiments, the tip further includes a supporting structurebonded to the inner layer, and the substrate and the supportingstructure are shaped to define an interior lumen.

In some embodiments, the substrate and the supporting structure areshaped to define a thimble that contains the interior lumen.

In some embodiments, the tip further includes a catheter configured forinsertion into a body of a subject, and the supporting structure iscoupled to a distal end of the catheter.

In some embodiments, the distal end of the catheter includes a flowdiverter configured to divert fluid received from a proximal end of thecatheter, and the supporting structure is coupled to the flow divertersuch that the flow diverter is disposed inside of the interior lumen.

In some embodiments, an average diameter of each of the narrowerchannels is between 5 and 50 microns.

In some embodiments, an average narrower-channel diameter of each of thenarrower channels is less than 50% of an average wider-5 channeldiameter of each of the wider channels.

In some embodiments, a thickness of the substrate is between 5 and 75microns.

In some embodiments, the apparatus further includes one or moreelectrically-conductive traces disposed on the inner surface andelectrically isolated from the inner layer, the substrate is shaped todefine respective holes opposite the traces, and the outer layerincludes a main portion; and one or more islands that are electricallyisolated from the main portion and contact the traces, respectively, byvirtue of at least partly filling the holes.

In some examples, there is provided an electrophysiology catheter tipthat includes a dual metal layered electrically and thermally-insulatingsubstrate including an outer layer of an thermally-conducting metal; aninner layer of an thermally-conducting metal; a polymer layer betweenthe inner and outer layer; and a plurality of thermal bridgesselectively positioned between the inner and outer layers and throughthe polymer layer increase the heat transfer of the catheter tip throughthe polymer layer such that when approximately 0.63 Amperes aredelivered to the outer layer tip, at least approximately 100%improvement in what is believed to be clinically safe ablation time isachieved as compared to a standard flex circuit ablation catheter withapproximately 0.63 Amperes and when approximately 0.90 Amperes aredelivered to the outer layer of the tip, at least approximately 100%improvement in what is believed to be clinically safe ablation timeversus a standard flex circuit ablation catheter with ablation currentof about 0.90 Amperes.

In some embodiments, the catheter tip comprises at least 1000 thermalbridges.

In some embodiments, the thermal bridges electrically and thermally jointhe inner and outer layers, thereby permitting heat transfer from theoutside to the inside of the catheter tip and temperatures are coolableby saline used during irrigation.

In some embodiments, the thermal bridges include solid cylinders,allowing irrigation liquid to transfer heat to the exterior (e.g.,plated irrigation holes that transfer heat both between the layers andto the liquid).

In some embodiments, a diameter of the thermal bridges is approximatelyabout 60 microns.

In some embodiments, distance between the bridges is about 0.2 to 0.3mm.

In some embodiments, the thermally-conducting metal of the inner layerand the outer layer are the same material.

In some embodiments, the thermally-conducting metal of the inner layerand the outer layer are different materials.

In some embodiments, the thermally-conducting metal of the inner andouter layers is gold and thickness of approximately about 40 microns.

In some embodiments, the polymer layer is a printed circuit board (PCB)having a thickness of approximately about 50 microns.

In some embodiments, the catheter tip is a distal tip of an ablationcatheter, further including a plurality of electrodes oriented tocontact cardiac tissue; and a plurality of irrigation holes between theinner and outer layers.

In some embodiments, the irrigation holes comprise heat transfer metalplated walls.

In some embodiments, a thickness of wall plating in the irrigation holesis approximately 25 microns.

In some embodiments, the catheter tip comprises a total shell thicknessof approximately 130 microns.

In some embodiments, the catheter tip is configured to generate a heatgenerated hemispherical ablation zone of at least approximately 2 mmradius.

In some embodiments, includes a cylindrical section; and a dome sectiondistal of the cylindrical section, wherein the thermal bridges arepositioned in the cylindrical and dome sections.

There is further provided, in accordance with some embodiments of thepresent disclosure, a method that includes inserting, into a body of asubject, a distal end of a catheter that includes a substrate having aninner surface, which is covered at least partly by an inner thermallyconductive layer, and an outer surface, which is covered at least partlyby an outer thermally conductive layer, the substrate being shaped todefine (i) multiple narrower channels, which pass between the innersurface and the outer surface and are filled by thermally conductivecolumns, and (ii) one or more thermally-plated wider channels that passbetween the inner surface and the outer surface. The method furtherincludes, subsequently to inserting the distal end of the catheter intothe body of the subject, contacting tissue of the subject with the outerthermally-conducting layer. The method further includes, whilecontacting the tissue, passing an electric current, via an outerthermally-conducting layer (which can be as low as 1 micron as long asit is overlaying a thicker thermally conductive layer), into the tissue,such that heat is generated in the tissue.

The method can provide for the inner and/or outer layers and theconnecting bridges and thermally-plated irrigation channels to act as asingle thermally conductive structure, so that the heat can be conductedfrom the tissue to this structure and dissipated convectively by theirrigation fluid and the blood in contact with this structure. In thisexample, as the heat is transferred mainly from the central part of theablation, this decreases the hot spot temperature without adverselyaffecting the extent of the thermal lesion in the tissue.

In some embodiments, the tissue includes cardiac tissue of the subject.

In some embodiments, the outer tip layer includes a main portion and oneor more islands that are electrically isolated from the main portion,and the method further includes, using the 10 islands, sensingelectrographic signals from the cardiac tissue.

There is further provided, in accordance with some embodiments of thepresent disclosure, a method that includes drilling multiple narrowerchannels, and one or more wider channels, through a flexiblethermally-insulating substrate, such that the narrower channels and thewider channels pass between an inner surface of the substrate and anouter surface of the substrate. The method further includes, using athermally-conducting material, at least partly covering the innersurface and the outer surface, completely filling the narrower channels,and plating the wider channels.

In some embodiments, the method includes at least partly covering theinner surface and the outer surface, completely filling the narrowerchannels, and plating the wider channels includes at least partlycovering the inner surface and the outer surface, completely filling thenarrower channels, and plating the wider channels by depositing thethermally conducting material onto the inner surface and the outersurface of the substrate, and into the narrower channels and the widerchannels; subsequently to depositing the thermally conducting materialonto the inner surface of the substrate, while the outer surface of thesubstrate is covered, plating the substrate in a plating bath of thethermally conducting material for a first time interval; subsequently toplating the substrate for the first time interval, at least partlyuncovering the outer surface of the substrate; and subsequently to atleast partly uncovering the outer surface of the substrate, plating thesubstrate in the plating bath for a second time interval.

In some embodiments, the method further includes bonding the thermallyconducting material that covers the inner surface to a supportingstructure; and shaping the substrate and the supporting structure todefine an interior lumen.

In some embodiments, shaping the substrate and the supporting structureincludes shaping the substrate and the supporting structure to define athimble that contains the interior lumen.

In some embodiments, the method further includes etching one or moreelectrically-conductive traces onto the inner surface of the substrate,depositing the thermally conducting material onto the inner surface ofthe substrate includes depositing the thermally conducting material ontothe inner surface of the substrate such that the electrically-conductivetraces remain electrically isolated from the thermally conductingmaterial, the method further includes forming holes in the substrateopposite the traces, respectively, and depositing the thermallyconducting material onto the outer surface of the substrate includesdepositing the thermally conducting material onto the outer surface ofthe substrate such as to form (i) a main portion, and (ii) one or moreislands that are electrically isolated from the main portion and contactthe traces, respectively, by virtue of at least partly filling theholes.

There is further provided, in accordance with some embodiments of thepresent disclosure, a method that includes inserting, into a body of asubject, a distal end of a catheter, the distal end including an outerlayer of an electrically and thermally-conducting material; an innerlayer of a thermally-conducting material; a polymer layer between theinner and outer layer; and a plurality of thermally conductive bridgesselectively positioned between the inner and outer layers and throughthe polymer layer thereby significantly increasing the heat transfer ofthe catheter tip through the polymer layer; subsequently to insertingthe distal end of the catheter into the body of the subject, contactingtissue of the subject with the outer layer; while contacting the tissue,passing an ablation current, via the outer layer, into the tissue. Partof the heat generated in the tissue is transferred thermal bridgethermally-conducting layer thermally-conducting layer via the thermallyconductive structure of two layers (inner and outer) connected bythermal bridges and finally convectively removed from the tip by theirrigation fluid and blood.

In some embodiments, the method further includes orienting the distalend of the catheter at some predetermined angle (e.g., 45°, 90°, etc.)to the tissue; penetrating the tissue to a penetration depth; ablatingtissue, through the distal end of the catheter, with the ablationcurrent/power for a predetermined duration of time under a predeterminedsafety temperature condition.

In some embodiments, the catheter tip penetration depth is approximatelyabout 0.8 mm.

In some embodiments, the step of ablating tissue results in a lesiondepth of approximately about 5.6 mm at ablation current about 0.63Amperes.

In some embodiments, the step of ablating tissue results in a lesionwidth of approximately about 8.9 mm at ablation current about 0.63Amperes.

In some embodiments, the predetermined safety temperature is less thanor equal to approximately about 130° C.

In some embodiments, the predetermined duration of time is at leastabout 30 s and the ablation current is about 0.63 Amperes whereby thethroughout ablation the catheter maintains an ablation zone less than orequal to approximately about 130° C. thereby avoiding tissue rupture.

In some embodiments, the step of ablating tissue results in at leastabout a 93% improvement in lesion width versus a standard flex circuitablation catheter where an ablation current is about 0.63 Amperes.

In some embodiments, the step of ablating tissue results in at leastabout a 500% improvement in what is believed to be clinically safeablation time versus a standard flex circuit ablation catheter where anablation current is about 0.63 Amperes.

In some embodiments, the step of ablating tissue results in at leastabout an 85% improvement in lesion depth versus a standard flex circuitablation catheter where an ablation current is about 0.63 Amperes.

In some embodiments, the predetermined duration of time is at leastabout 5 s and the ablation current is about 0.90 Amperes whereby thethroughout ablation the catheter maintains an ablation zone less than orequal to approximately about 130° C. thereby avoiding tissue rupture.

In some embodiments, the step of ablating tissue results in at leastabout a 60% improvement in lesion width versus a standard flex circuitablation catheter where an ablation current is about 0.90 Amperes.

In some embodiments, the step of ablating tissue results in at leastabout a 160% improvement in what is believed to be clinically safeablation time versus a standard flex circuit ablation catheter where anablation current is about 0.90 Amperes.

In some embodiments, the step of ablating tissue results in at leastabout an 38% improvement in lesion depth versus a standard flex circuitablation catheter where an ablation current is about 0.90 Amperes.

In some embodiments, the step of ablating tissue results in a lesiondepth of approximately about 3.6 mm at ablation current about 0.90Amperes.

In some embodiments, the step of ablating tissue results in a lesionwidth of approximately about 6.9 mm at ablation current about 0.90Amperes.

There is further provided, in accordance with some embodiments of thepresent disclosure, a method that includes drilling a plurality ofthermal bridges, through a flexible thermally-insulating polymersubstrate; and using a thermally-conducting metal to sandwich theflexible thermally-insulating polymer substrate between an inner surfaceand an outer surface.

In some embodiments, the step of drilling the thermal bridges comprisesdrilling at least 1,000 thermal bridges

In some embodiments, the method further includes drilling a plurality ofirrigation holes through the inner and outer layers and thethermally-insulating polymer substrate, the irrigation holes having adiameter larger than the thermal bridges.

The present disclosure will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system for ablating tissue of asubject, in accordance with some embodiments of the present disclosure;

FIG. 2A is a schematic illustration of a distal tip of a catheter, inaccordance with some embodiments of the present disclosure;

FIG. 2B schematically illustrates a cross-section through a portion of acatheter tip electrode, in accordance with some embodiments 10 of thepresent disclosure;

FIG. 3 schematically illustrates a longitudinal cross-section throughthe distal tip shown in FIG. 2A, in accordance with some embodiments ofthe present disclosure;

FIG. 4 is a flow diagram for a method of manufacturing a catheter tipelectrode, in accordance with some embodiments of the presentdisclosure;

FIG. 5 is a schematic illustration of a catheter tip electrode prior tothe deformation thereof, in accordance with some embodiments of thepresent disclosure;

FIG. 6 is a schematic illustration of a distal tip of a catheter, inaccordance with some embodiments of the present disclosure;

FIG. 7A is a schematic illustration of a distal tip of a catheter, inaccordance with some embodiments of the present disclosure;

FIG. 7B schematically illustrates a cross-section through a portion of acatheter tip electrode, in accordance with some embodiments of thepresent disclosure;

FIG. 8 is a schematic illustration of a distal tip of a catheter, inaccordance with some embodiments of the present disclosure;

FIG. 9 depicts a temperature field at approximately 130° C. maximum withstandard flex circuit;

FIG. 10 depicts a temperature field at approximately 130° C. maximumwith dual metal layers;

FIG. 11 depicts a temperature field at approximately 130° C. maximumwith standard flex circuit;

FIG. 12 depicts a temperature field at approximately 130° C. maximumwith dual metal layers;

FIG. 13 depicts a heat flux map for the distal tip of this disclosurewith dual metal layers and constructed with platinum and connected byvias through an example printed circuit board;

FIG. 14 depicts a temperature map with dual metal layers and constructedwith platinum and connected by thermal vias through an example printedcircuit board;

FIG. 15 depicts a graph summarizing maximum temperature in the tissueduring ablation as between the standard flex circuit and dual metallayered distal catheter tips;

FIG. 16 depicts a graph summarizing maximum temperature in the tissueduring ablation as between standard flex circuit and dual metal layereddistal catheter tips;

FIG. 17 depicts a perspective view of heat generated in a hemisphereunder an example embodiment of the dual metal layered distal tip of thecatheter;

FIG. 18 depicts a perspective view of an example embodiment of the dualmetal layered distal tip of the catheter in contact with tissue;

FIG. 19 is a flow diagram for a method in accordance with someembodiments of the present disclosure; and

FIG. 20 is a flow diagram for a method of manufacturing a catheter tipelectrode, in accordance with some embodiments of the presentdisclosure.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Embodiments of the present disclosure include an ablation electrodecomprising at least one flexible printed circuit board (PCB) that isbonded, by an adhesive, to a supporting metallic sheet. The flexible PCBcomprises a flexible thermally-insulating substrate comprising an outersurface that is coated by an outer layer of an electrically-conducting(and biocompatible) metal, such as gold, palladium, or platinum, and aninner surface that is coated by an inner layer of the same (and/oranother) thermally-conducting metal. The inner surface may furthersupport one or more electric components such as sensors (e.g.,thermocouples) and traces, which are electrically isolated from theinner thermally-conducting layer. Following the deposition of theelectric components, the coating of the substrate, and the bonding ofthe PCB to the supporting sheet, the flexible PCB (together with thesupporting sheet) may be deformed into any suitable shape. For example,in some embodiments, the flexible PCB is deformed into a thimble-shapedelectrode, referred to hereinbelow as a “tip electrode.” The electrodeis then coupled to the distal end of a catheter.

During an ablation procedure, the outer thermally-conducting layer isbrought into contact with the tissue that is to be ablated, and ablatingcurrents are then passed, via the outer thermally-conducting layer, intothe tissue. While the ablating currents are applied to the tissue, thesensors may acquire any relevant physiological readings from the tissue.Typically, open, plated vias, which pass through the electrode, provideelectrical connectivity between the inner and outer thermally-conductinglayers, such that the ablating currents may pass outward through theplated vias, and electrographic signals from the tissue may pass inwardthrough the plated vias. Electrical connectivity may also be provided byblind vias, each such via being formed by the removal of a portion ofthe substrate such that the outer thermally-conducting layer directlycontacts a trace underneath.

The aforementioned plated vias also provide fluid communication betweenthe inner and outer surfaces of the electrode, such that an irrigatingfluid (e.g., saline) may pass through the plated vias into thesurrounding blood. The irrigating fluid evacuates heat from the interiorof the electrode into the blood, and additionally dilutes the blood atthe tissue-electrode interface, thus reducing the probability ofcoagulum or charring. Due to the fact that the plated vias provide forpassage of the irrigating fluid therethrough, the plated vias may alsobe referred to as “irrigation channels” or “irrigation holes.”

A challenge, when using the type of electrode described above, is thatthe substrate may provide significant thermal resistance, such as tolimit the amount of heat that is transferred from the tissue-electrodeinterface to the interior of the electrode. This, in turn, limits theamount of heat that may be evacuated by the irrigating fluid.

To address this challenge, embodiments described herein provide a largenumber (e.g., tens of thousands) of small, closed vias, referred tohereinbelow as “thermal vias,” that increase the thermal connectivitybetween the two surfaces of the electrode. Such thermal vias maycomprise, for example, columns of a thermally-conducting metal, such asgold, that connect the outer thermally-conducting layer to the innerthermally-conducting layer. Typically, the thermal vias are distributedover the entire surface of the electrode. The thermal vias increase theamount of heat that is transferred to the interior of the electrode,thus facilitating the evacuation of heat by the irrigating fluid.

Embodiments of the present disclosure also include a manufacturingprocess for the electrode. Typically, both surfaces of the substrate areinitially coated with copper; hence, the manufacture of the electrodetypically begins with the etching away of this copper, except for wherecopper traces are required on the inner surface of the substrate. Next,constantan traces, to be used for thermocouples, are deposited onto theinner surface. Subsequently, one or more wide channels, a large numberof relatively narrow channels, and, optionally, one or more blind vias,are drilled through the substrate.

Subsequently, on the inner surface of the substrate, a mask is appliedover the traces and the surrounding exclusion zones that will insulatethe traces from the inner thermally-conducting layer. (The mask is notapplied over the portions of the constantan traces that are designatedas thermocouple junctions.) Similarly, on the outer surface, anothermask is applied over exclusion zones that will insulate microelectrode“islands” from the rest of the outer thermally-conducting layer.

Next, a thin layer of metal (typically gold) is sputtered into thechannels and onto both surfaces of the substrate. The metal sputteredonto the inner surface includes traces that intersect the constantantraces, thus forming thermocouple junctions. Following the sputtering ofthe metal, the masks are removed, the interior traces and exclusionzones are covered by another mask, and the entire outer surface is alsomasked.

Subsequently, the substrate is placed in a plating bath for a period oftime, such that (i) any remaining exposed portions of the inner surfaceof the substrate are covered by the metal, i.e., the layer of metalexpands laterally over the inner surface, (ii) the thickness of theinner layer is increased, (iii) the narrow channels are sealed shut,thus becoming thermal vias, and (iv) the wide channels are narrowed,thus becoming plated irrigation channels. The interior and exteriorsurfaces are then unmasked. Next, the interior traces and exclusionzones are covered by at least one coverlay.

Subsequently, the substrate is returned to the plating bath for anotherperiod of time, such that the thickness of both the outer layer andinner layer are increased, and the plated irrigation channels arenarrowed. Typically, the total duration of time for which the substrateremains in the plating bath is set such that the thickness of the innerlayer reaches the thickness of the coverlay. (Typically, the thicknessof the outer layer is not increased significantly, so as to reduce therisk of the outer layer cracking when the substrate is folded into itsfinal shape.)

Next, apertures, which have a diameter greater or equal to that that ofthe irrigation holes, are drilled through a supporting sheet of metal,comprising, for example, an alloy of cobalt chromium. The supportingsheet is then bonded to the inner thermally-conducting layer and thecoverlay, such that the apertures in the supporting sheet are alignedwith the irrigation channels in the substrate. Subsequently, the platedsubstrate and supporting sheet are deformed into their desired shape.Finally, the relevant wires are connected to the electrode, and theelectrode is then coupled to the catheter.

System Description

Reference is initially made to FIG. 1 , which is a schematicillustration of a system 20 for ablating tissue of a subject 26, inaccordance with some embodiments of the present disclosure.

FIG. 1 depicts a physician 28 performing a unipolar ablation procedureon subject 26, using an ablation catheter 22. In this procedure,physician 28 first inserts the distal tip 32 of catheter 22 into thesubject, and then navigates distal tip 32 to the tissue that is to beablated. For example, the physician may advance the distal tip throughthe vasculature of the subject until the distal tip is in contact withcardiac tissue belonging to the heart 24 of the subject. Next, whiledistal tip 32 contacts the tissue, the physician causes radiofrequency(RF) electric currents to be passed between distal tip 32 and a neutralelectrode patch 30 that is coupled externally to the subject, e.g., tothe subject's back.

To facilitate navigating the catheter, catheter 22 may comprise one ormore electromagnetic position sensors, which, in the presence of anexternal magnetic field, generate signals that vary with the positionsof the sensors. Alternatively or additionally, any other suitabletracking system, such as an impedance-based tracking system, may beused. For example, both electromagnetic tracking and impedance-basedtracking may be used, as described, for example, in U.S. Pat. No.8,456,182, whose disclosure is incorporated herein by reference.

Catheter 22 is proximally connected to a console 34, comprising, forexample, a processor (PROC) 23, a pump 25, and a signal generator (GEN)27. (Electrode patch 30 is typically also connected to console 34, via awire 42.) During the ablation procedure, signal generator 27 generatesthe aforementioned ablating currents. These currents are carried throughcatheter 22, over one or more wires, to distal tip 32. Additionally,pump 25 supplies an irrigating fluid, such as saline, to the distal tipof the catheter, as further described below with reference to FIGS. 2A-Band FIG. 3 .

Console 34 further comprises controls 35, which may be used by thephysician to control the parameters of the ablating currents. Inparticular, in response to the manipulation of controls 35 by physician28, processor 23 may adjust the parameters of the ablating currents, byoutputting appropriate instructions to signal generator 27 over anysuitable wired or wireless communication interface. Processor 23 maysimilarly control pump 25 over any suitable wired or wireless interface.In addition, the processor may receive and process any relevant signalsfrom the distal tip of the catheter, such as the signals received fromany of the sensors described herein.

In some embodiments, system further comprises a display 38, which maydisplay relevant output to physician 28 during the procedure.

Notwithstanding the particular type of procedure depicted in FIG. 1 , itis noted that the embodiments described herein may be applied to anysuitable type of ablation procedure, or any other procedure thatnecessitates the transfer of heat through a flexible PCB.

The Distal Tip of the Catheter

Reference is now made to FIG. 2A, which is a schematic illustration ofdistal tip 32, in accordance with some embodiments of the presentdisclosure. Reference is additionally made to FIG. 3 , whichschematically illustrates a longitudinal cross-section through distaltip 32, in accordance with some embodiments of the present disclosure.

Distal tip 32 comprises at least one ablation electrode 40, 30 such asthe catheter tip electrode depicted in FIG. 2A and FIG. 3 . Electrode 40comprises a plated flexible thermally-insulating substrate 41 that isbonded, by an adhesive, to a supporting structure 36 at the distal endof catheter 22. Substrate 41 may be made of any suitable flexiblethermally-insulating material, such as a flexible polymer (e.g.,polyimide) or liquid crystal polymer (LCP). Supporting structure 36 maybe made of any suitably strong material, such as cobalt chromium,stainless steel, magnesium, and/or an alloy of any of the above. Forexample, supporting structure 36 may comprise the L-605cobalt-chromium-tungsten-nickel alloy.

In general, electrode 40 may have any suitable shape. In someembodiments, as shown in FIG. 2A and FIG. 3 , electrode 40 isthimble-shaped, comprising a cylindrical portion 40 b that is capped bya dome-shaped portion 40 a. Typically, tabs 47 at the proximal end ofthe electrode comprise soldering pads onto which wires, which runthrough the length of the catheter, may be soldered, such as toestablish electrical connectivity between the electrode and the proximalend of the catheter. These soldering pads are described in furtherdetail below, with reference to FIGS. 4-5 .

As shown in the “A-A” cross-section of FIG. 2A, substrate 41 comprisesan inner surface 76, which faces supporting structure 36, and an outersurface 45, which faces away from supporting structure 36. Typically,the thickness T0 of the substrate—i.e., the distance between the innerand outer surfaces of the substrate—is between 5 and 75 (e.g., between12 and 50) microns. At least part of the inner surface is covered by aninner layer 70 of a thermally-conducting metal, such as gold. Typically,inner layer 70 has a thickness T1 of between 10 and 50 microns.Similarly, at least part of outer surface 45 is covered by an outerlayer 50 of the metal. Typically, outer layer 50 has a thickness T2 ofbetween 1 and 5 microns.

Typically, outer layer 50 is discontinuous, in that the outer layercomprises a main portion 54 along with one or more isolated portionsthat are electrically isolated from main portion 54 by exposed portionsof the substrate. These isolated portions may include one or more“islands” that function as sensing microelectrodes 56. For example,outer layer 50 may comprise 3-7 microelectrodes 56 distributed aroundthe circumference of the distal tip. Alternatively or additionally, theisolated portions may comprise a sensing ring electrode 43, which may bedisposed, for example, near the proximal end of distal tip 32.

A respective electrically-conductive trace 78, which is electricallyisolated from inner layer 70 by an exposed portion of inner surface 76,is disposed beneath each of the sensing electrodes. As further describedbelow with reference to FIG. 4 , prior to forming the sensingelectrodes, holes, referred to herein as blind vias 80, are formed(e.g., drilled) in the substrate above traces 78. Subsequently, as thesensing electrodes are deposited onto the outer surface of thesubstrate, the sensing electrodes at least partly fill blind vias 80,thus contacting the traces.

Hence, during the procedure, electrographic signals from the cardiactissue of the subject that are sensed by the sensing electrodes may becarried over traces 78 to wires that run through catheter 22 to theproximal end of the catheter. The signals may thus be delivered toprocessor 23 for analysis.

Reference is now additionally made to FIG. 2B, which schematicallyillustrates a cross-section through a portion of electrode 40, inaccordance with some embodiments of the present disclosure. FIG. 2Bcorresponds to the “B-B” cross-section indicated in FIG. 2A.

Substrate 41 is shaped to define a plurality of channels, includingmultiple narrower channels 46 and one or more wider channels 44, thatpass between the inner and outer surfaces of the substrate. Typically,each channel is tapered along the length of the channel, with thecross-sectional area of the channel at the inner surface of thesubstrate being slightly greater than the cross-sectional area at theouter surface. The cross-sectional area (or average cross-sectionalarea) of each narrower channel 46 is less than that of each widerchannel 44.

In some embodiments, the channels have a circular cross-section. In suchembodiments, the average diameter d0 of each of the narrower channelsmay be less than 50% (e.g., less than 25%) of the average diameter d1 ofeach of the wider channels. Alternatively or additionally, diameter d0may be between 5 and 50 (e.g., between 5 and 30) microns, and/ordiameter d1 may be between 50 and 300 microns. In other embodiments, atleast some of the channels may have a cross-section having a squareshape, or any other suitable shape. (In such embodiments, the averagecross-sectional area of each of the channels may correspond to 10 thatimplied above by the ranges for d0 and d1.)

Typically, the electrode includes 30-100 wider channels. Each widerchannel 44 is plated by a plating layer 52 of the electrically andthermally conducting metal, which connects outer layer 50 to inner layer70. The plated wider channels thus provide electrical and thermalconductivity between the outer and inner layers of metal. Moreover, theplated wider channels provide a fluid passageway between the interiorand exterior of distal tip 32, such that an irrigating fluid 39,supplied by pump 25 (FIG. 1 ), may flow therethrough. Hence, the platedwider channels may be referred to as “irrigation holes” 72. (Thediameter of each irrigation hole is smaller than diameter d1 byapproximately twice the thickness of plating layer 52.) Supportingstructure 36 is shaped to define apertures 62 that are aligned withirrigation holes 72, such that the supporting structure does notobstruct the irrigation holes.

Typically, the number of narrower channels 46 is relatively large. Forexample, substrate 41 may be shaped to define at least 1,000, 5,000,10,000, or 20,000 narrower channels. Alternatively or additionally, theratio of narrower channels to wider channels may be at least 300:1.Alternatively or additionally, the total area of the respective outeropenings of the narrower channels (i.e., the openings of the narrowerchannels at the outer surface of the substrate) may be at least 10%,20%, or 30% of the area of the outer surface of the substrate. Thus, forexample, if the area of the outer surface of the substrate (includingthe narrower channels) is 27 mm², and each of the narrower channelsincludes a circular outer opening having a diameter of 25 microns (andhence an area of 0.0005 mm²), the number of narrower channels may beapproximately 16,500 (for a total area of 8.1 mm²), such that the outeropenings of the narrower channels cover approximately 30% of the outersurface.

In contrast to the wider channels, narrower channels 46 are not merelyplated, but rather, are filled by respective columns 48 of thethermally-conducting metal, which connect outer layer 50 to inner layer70. (Columns 48 are not necessarily cylindrical, since, as noted above,narrower channels 46 do not necessarily have a circular cross-section.Furthermore, as noted above, the cross-sectional area of each column mayvary along the length of 15 the column.

It is noted that outer layer 50, inner layer 70, plating layer 52 andcolumns 48 may be collectively described as a single body of metal thatcovers the substrate.) Due to the large number of channels 46, and byvirtue of each of these channels being filled, a large amount of heatmay be transferred via channels 46. Hence, the filled narrower channelsmay be referred to as “thermal vias” 74. (For ease of illustration, nothermal vias are shown in the “A-A” cross section of FIG. 2A.)

Notwithstanding the above, it is noted that in some embodiments, thenarrower channels are not filled, but rather, are merely plated,similarly to the wider channels. Even in such embodiments, a largeamount of heat may be transferred to the interior of the electrode.

Typically, catheter 22 comprises a fluid-delivery tube (not shown),which runs through the full length of the tubular body 22 m of catheter22. The fluid-delivery tube is distally coupled to a flow diverter 60that is shaped to define one or more fluid-flow apertures 64. Flowdiverter 60 diverts fluid 39, which is received, via the fluid-deliverytube, from the proximal end of the catheter, through fluid-flowapertures 64. In such embodiments, electrode 40 may be coupled to thebase 58 of flow diverter 60, such that the flow diverter is disposedinside of the interior lumen of the electrode. For example, supportingstructure 36 may be bonded to base 58. Alternatively or additionally,base 58 may be shaped to define a plurality of protrusions, andsupporting structure 36 may be shaped to define a plurality ofcomplementary holes, such that the protrusions snap into the holes.

As described above with reference to FIG. 1 , during the ablationprocedure, physician 28 contacts tissue of subject 26 with distal tip32, and in particular, with outer layer 50. While contacting the tissuewith outer layer 50, the physician passes electric currents, via theouter layer, into the tissue. The electric currents cause heat to begenerated in the tissue, such that a lesion is formed in the tissue.This heat is transferred, via thermal vias 74 (i.e., via columns 48) toinner layer 70. At the same time, pump 25 (FIG. 1 ) pumps irrigatingfluid 39 through the fluid-delivery tube, such that the fluid flows intothe interior of the electrode through fluid-flow apertures 64 of flowdiverter 60. This fluid then flows out of the distal tip throughapertures 62 and irrigation holes 72, thus evacuating the heat frominner layer 70 into the subject's blood.

Manufacturing the Distal Tip

Reference is now made to FIG. 4 , which is a flow diagram for a method400 of manufacturing electrode 40, in accordance with some embodimentsof the present disclosure. Reference is additionally made to FIG. 5 ,which is a schematic illustration of electrode 40 prior to thedeformation thereof, in accordance with some embodiments of the presentdisclosure. (FIG. 5 shows the interior of electrode 40, i.e., thevarious elements that are coupled to the inner surface of substrate 41.)

FIG. 4 assumes that at least the inner surface of the substrate isinitially coated with a layer of copper. Hence, method 400 begins withan etching step 84, in which all of the copper is etched away from theinner surface, with the exception of copper traces 114, which are to beconnected to the sensing electrodes on the exterior of the electrode.(Any copper on the 5 outer surface is also etched away.) This etchingmay be performed, for example, by placing a mask over the portions ofthe copper that are designated for traces 114, and then chemicallyremoving the exposed copper. Alternatively, if the inner surface of thesubstrate is initially exposed, copper traces 114 may be deposited ontothe inner surface.

Subsequently, at a trace-depositing step 86, constantan traces 118,which are to be used for thermocouples, are deposited onto the innersurface of the substrate. Trace-depositing step 86 may be performed, forexample, by physical vapor deposition (PVD), such as sputter deposition.For example, a mask may be placed over the entire inner surface, withthe exception of those portions of the inner surface that are designatedfor constantan traces 118. Subsequently, a seed layer of a base metal,such as titanium-tungsten, may be sputtered onto the substrate. Finally,the constantan may be sputtered over the base metal.

Typically, to minimize the required wiring, the constantan tracesterminate at a common constantan-trace soldering pad 120. In someembodiments, prior to the deposition of the constantan, a hole (or“stake via”) is drilled through the substrate at the site of solderingpad 120. Subsequently, the deposited constantan fills the hole, and thenforms soldering pad 120 above the hole. Alternatively, instead ofdrilling completely through the substrate, a depression may be drilledinto the substrate, such that the deposited constantan fills thedepression. In either case, soldering pad 120 is “staked” to thesubstrate by the constantan underneath the soldering pad. (To facilitatethe filling of the hole or depression, a draft angle may be used totaper the hole or depression, as described immediately below for thenarrower and wider channels.)

Next, at a drilling step 88, multiple narrower channels and one or morewider channels 44 are drilled through the substrate, typically usinglaser drilling. (The wider channels, but not the narrower channels, maybe seen in FIG. 5 .) Typically, the channels are drilled from the innersurface of the substrate, using a draft angle such that the channelsnarrow as they approach the outer surface; this facilitates thecollection of metal onto the walls of the channels during the subsequentsputtering process. In addition, blind vias 80 may be drilled (e.g.,laser-drilled) through the substrate from the outer surface of thesubstrate at those portions of the outer surface that are designated forsensing electrodes, using copper traces 114 as stops. (In other words,portions of the substrate that are disposed over the copper traces maybe removed, thus exposing the copper traces.) Typically, a draft angleis used for the blind vias, such that the blind vias narrow as theyapproach the inner surface of the substrate; this facilitates thecollection of metal onto the walls of the blind vias.

Next, at a first masking step 90, the copper and constantan traces,along with exclusion zones 91 (i.e., exposed portions of the innersurface of the substrate) that are designated for insulating thesetraces, are masked. (Portions of the constantan traces that aredesignated for the thermocouple junctions are not masked.) Additionalexclusion zones designated for insulating the gold traces that willintersect the constantan traces (thus forming constantan-goldthermocouples) are also masked. Additionally, exclusion zones on theouter surface that are designated for insulating the sensing electrodesare masked.

Subsequently, at a depositing step 92, a thin layer of gold 30 isdeposited onto the inner and outer surfaces of the substrate and intothe channels. Depositing step 92 may be performed, for example, byphysical vapor deposition (PVD), such as sputter deposition. (Typically,a seed layer of a base metal, such as titanium-tungsten, is sputteredonto the substrate prior to the sputtering of the gold.) By virtue ofthe masks, the gold is not deposited onto the traces or exclusion zones.

The deposited gold includes an initializing layer for inner layer 70,outer layer 50, plating layer 52, and columns 48. The deposited goldfurther includes gold traces 122 that cover the constantan traces atthermocouple junctions 124. Each gold trace 122 terminates at arespective gold-trace soldering pad 126. The deposited gold furtherincludes a respective copper-trace soldering pad 116 for each of thecopper traces. In some embodiments, copper-trace soldering pads 116and/or gold-trace soldering pads 126 are staked to the substrate, asdescribed above for the constantan-trace soldering pad. The depositedgold further includes at least one gold soldering pad 128, which isconnected to inner layer 70. Gold soldering pad 128 may also be stakedto the substrate.

Following the deposition, the masks (along with any gold that wasdeposited onto the masks) are removed at a mask-removing step 93.Subsequently, at a second masking step 94, the traces, the inner-surfaceexclusion zones that surround the traces, and the entire outer surfaceof the substrate are masked.

Following second masking step 94, while the traces and outer surfaceremain masked, the substrate is plated in a plating bath of gold for afirst time interval, at a first plating step 98. The plating of thesubstrate causes any gaps in the gold to be filled, and furtherincreases the thickness of the gold, such that, for example, inner layer70 reaches a thickness of between 5 and 40 microns, while the diameterof the wider channels is reduced to between 30 and 200 microns.Additionally, the narrower channels may become completely filled.

Typically, the plating of the substrate is electrochemical, whereby theflow of electric current through the gold that already coats thesubstrate causes this gold to attract gold ions in the plating bath. Theamplitude and duration of the current may be controlled such that thegold reaches the desired thickness.

Following first plating step 98, the inner and outer surfaces of thesubstrate, with the exception of the aforementioned exclusion zonesdesignated to insulate the sensing electrodes, are unmasked, at anunmasking step 100. Next, at a coverlay-applying step 101, at least onecoverlay 130 is applied over the traces and inner-surface exclusionzones. (In some embodiments, as illustrated in the inset portion of FIG.5 , coverlay 130 is transparent or nearly transparent.)

Typically, the proximal portion of coverlay 130 that covers 10 tabs 47is shaped to define windows 132 that expose the soldering pads, suchthat the soldering pads may be thickened during the subsequent platingprocess. (An additional cover 142, having windows that are aligned withwindows 132, may cover the proximal portion of the coverlay.) Typically,the soldering pads are not completely exposed, but rather, are held“captive” by coverlay 130, in that one or more edges of each solderingpad are covered by the rims of windows 132. Coverlay 130 thus helps holdthe soldering pads to substrate 41 during the subsequent solderingprocess.

Subsequently, at a second plating step 102, the substrate is plated inthe plating bath for a second time interval, such that any gaps in outerlayer 50 are filled, while the inner, outer, and plating layers arethickened. For example, the second plating may increase the thickness ofthe inner layer to between 10 and 50 microns, while reducing thediameter of the wider channels to between 15 and 150 microns. Typically,the final thickness of the inner layer is the same as the thickness ofthe coverlay, such as to attain a smooth interior surface. (To avoid anyconfusion, the term “interior surface” is used herein to refer to thesurface that is formed by the coverlay and the inner gold layer, whereasthe term “inner surface” is used to refer to the underlying surface ofthe substrate.) Additionally, in the event that the narrower channelswere not completely filled during first plating step 98, these channelsare completely filled during second plating step 102. As in the case offirst plating step 98, the amplitude and duration of the electriccurrent in the plating bath may be controlled such that the desiredthicknesses are attained. (In some embodiments, the outer surface ismasked prior to depositing step 92, such that no gold is deposited ontothe outer surface during depositing step 92. In such embodiments,following unmasking step 100 and prior to second plating step 102, athin layer of gold is deposited onto the outer surface.)

Subsequently to second plating step 102, at an aperture-drilling step104, apertures 62 are drilled through supporting structure 36.(Alternatively to drilling, any other suitable technique, such aschemical etching, may be used to form the apertures.) Next, at a bondingstep 106, by the application of a suitable adhesive between supportingstructure 36 and the smooth interior surface that is formed by coverlay130 and inner layer 70, the supporting structure is bonded to theinterior surface, with apertures 62 being aligned with irrigation holes72. Typically, the area of the apertures is greater than that of theirrigation holes, such as to compensate for any small misalignments whenbonding the supporting structure.

Next, at a deforming step 108, electrode 40 is deformed into the desiredshape. For example, the electrode may be inserted into a forming jigthat shapes the electrode around a suitable mandrel. Following theinsertion of the electrode into the jig, the jig is placed inside anoven. Subsequently, the oven heats the electrode to a suitabletemperature, while pressure is applied to the electrode. The combinationof heat and pressure causes the electrode to bond to itself in thedesired shape.

In general, the substrate and supporting structure may be deformed intoany desired shape. Typically, however, during deforming step 108, thesubstrate and supporting structure are shaped to define an interiorlumen; for example, the substrate and supporting structure may be shapedto define a thimble that contains an interior lumen, as described abovewith reference to FIG. 2A and FIG. 3 . Alternatively, for example, thesubstrate and supporting structure may be shaped to define a ring.

Typically, to facilitate the manufacture of a thimble-shaped electrode,substrate 41 comprises two portions that are continuous with oneanother: a distal, circular portion 41 a, and a proximal, rectangularportion 41 b. Similarly, supporting structure 36 comprises two portionsthat are continuous with one another: a distal supporting portion 36 a,typically comprising a plurality of spokes 134 that radiate from acentral hub 136, and a proximal supporting portion 36 b. During bondingstep 106, distal supporting portion 36 a is bonded to the interiorsurface of circular portion 41 a, and the adhesive is applied to theouter surfaces of spokes 134. (These surfaces are opposite the surfacesshown in FIG. 5 .) In addition, proximal supporting portion 36 b isbonded to the interior surface of rectangular portion 41 b, leaving somedistal portions of this interior surface exposed. The adhesive isapplied to the outer surface of an overhanging tab 138 of proximalsupporting portion 36 b, which hangs over the side of rectangularportion 41 b. (Proximal supporting portion 36 b may also hang over theproximal end of rectangular portion 41 b.)

Subsequently, during deforming step 108, distal supporting portion 36 aand circular portion 41 a are folded over the top of the mandrel, whileproximal supporting portion 36 b and rectangular portion 41 b are rolledaround the mandrel. To maintain this configuration, the outer surfacesof spokes 134 are bonded to the exposed distal portions of the interiorsurface of rectangular portion 41 b, and the outer surface of tab 138 isbonded to the opposite end of proximal supporting portion 36 b.(Additionally, the inner surface of at least one of the spokes may bondto tab 138.) Thus, distal supporting portion 36 a and circular portion41 a are formed into dome-shaped portion 40 a (FIG. 2A), while proximalsupporting portion 36 b and rectangular portion 41 b are formed intocylindrical portion 40 b.

Subsequently, at a soldering step 110, wires are soldered onto thesoldering pads. In particular, the wire that delivers RF currents fromgenerator 27 (FIG. 1 ) is soldered onto gold soldering pad 128, whileother wires, which deliver signals to processor 23, are soldered to theother soldering pads.

Finally, at a coupling step 112, the electrode is coupled to thecatheter. For example, proximal supporting portion 36 b may be bonded tobase 58 of the flow diverter (FIG. 3 ). Alternatively or additionally,as described above with reference to FIG. 3 , protrusions belonging tobase 58 may snap into complementary holes 140 in proximal supportingportion 36 b. Subsequently, the flow diverter may be coupled to thefluid-delivery tube belonging to the catheter. (Alternatively, the flowdiverter may be coupled to the fluid-delivery tube before the electrodeis coupled to the flow diverter.)

Certain known ablation catheters are constructed from a double-sidedflexible circuit, and the exterior metal of the circuit is used to forma catheter tip electrode that is used for ablation. However, a polymerlayer between the exterior metal and the interior metal in these knownapproaches can create significant thermal resistance and serve to keepthe exterior surface temperature elevated. One solution to these andother problems is shown in FIGS. 6-8 , whereby the depicted solutionsignificantly increases the heat transfer through the polymer layer(e.g., PCB) through a plurality of thermal vias 80 (e.g., thousands ofvias 80) formed in the polymer layer. The vias 80 electrically andthermally join the exterior metal layer 70 to the interior metal layer50 of the example described in FIGS. 6-8 , thereby allowing heattransfer from the outside to the inside where temperatures of tip 32 canbe cooled by the saline used for irrigation. The vias 80 shown in FIGS.6-8 may be solid cylinders, typically of gold, or at least some may beplated through vias, allowing irrigation liquid to transfer to theexterior.

Layers 50, 70 are thermally conducting and particularly effective fortransferring out of the tissue at least because the heat flow from thecentral (and hottest) region of the ablation zone is criticallydependent on the thermal conductivity of the tip 32 as it is positionedabove the hottest part of the tissue. In turn, the heat flow through thecatheter tip 32 is increased, including into the fluid (e.g., irrigationand/or blood), by providing a thermal pathway from the tissue. The heatcomes from the outside, and the outer thermally conductive layer 70passes some of it directly to the blood. Part of the heat flows throughthe thermal bridges, as described more particularly below. In thisrespect, the herein described plated irrigation holes transfer some ofthe heat into the irrigation fluid, to the inner layer 50 and the innerlayer 50 can transfer the remaining heat to the irrigation fluid throughits surface. The irrigation fluid flowing through the plated holes losesome heat to the walls of the irrigation holes and mostly to the bloodafter exiting the catheter tip 32.

The purpose of the thermally-conducting layers 50, 70 is to increase theflow of heat there inside thus providing the greatest contact area withthe cooling fluid flow (e.g., blood, irrigation, etc.). Layers 50, 70are also effective at efficient heat transfer between layers to increasethe contact area. Layers 50, 70 are also effective at emulatingstructure of an all-metal tip, where the cooling occurs from all thesurfaces exposed to the liquid.

In particular, FIG. 6 depicts a perspective view of an exampleconstruction distal tip 32 of ablation catheter 22 of this disclosure.As discussed more particularly below, tip 32 can include a PCB 160(shown more particularly in FIGS. 7A-B) attached or otherwise formedwith dome-shaped portion 40 a and cylindrical portion 40 b. For example,PCB 160 can be wrapped with inner layer 70 and outer layer 50 withirrigation holes 72 and corresponding electrodes of tip 32 facing theinternal tissue of heart 24. The configuration of distal tip 32 shown inFIG. 6 is an example configuration that is chosen purely for the sake ofconceptual clarity. In alternative embodiments, any other suitableconfiguration can be used.

FIGS. 7A-8 depict an example distal tip 32 construction of the ablationcatheter 22 of this disclosure. In particular, FIG. 7A shows an innerperspective view of distal tip 32 at cross-section along centerline ofthe distal tip 32 to show the inner surface of the catheter tip 32 whileFIG. 8 depicts an outer perspective view of the same example tip 32. Itcan be seen that tip 32 in the illustrated example includes cylindricalportion 40 b and dome-shaped portion 40 b, each of which includeselectively positioned irrigation holes 72 and blind vias 80. Blind vias80 can be provided for electrical conductivity so inner layer 70 is indirect contact with outer layer 70 and one example distance between eachblind via 80 can be approximately about 0.2 to 0.3 mm. Irrigation holes72 of the depicted example can be heat transfer vias by themselves(e.g., be gold-plated walls).

Reference is now made to FIG. 7B, which schematically illustrates aclose-up longitudinal cross-section at C-C through distal tip 32. As canbe seen, the depicted example is dual metal layered whereby inner layer70 and outer layer 50 are shown and constructed from metal. Sandwichedtherebetween can be a PCB 160 with a plurality of selectively positionedvias 80 (e.g., thermal bridges). The inner and outer layers 70, 50 canbe constructed from gold and typical thickness for each can beapproximately about 40 microns. A typical diameter of the vias 80 inthis example can be approximately about 60 microns. A typical thicknessof the wall plating in the irrigation holes 72 of this example can beapproximately about 25 microns. A typical thickness of the PCB layer 160of this example can be approximately about 50 microns. A total shellthickness of the catheter tip 32 illustrated in FIG. 7A can therefore beapproximately about 130 microns (i.e. 0.13 mm).

Various aspects of the disclosed solution may be still more fullyunderstood from the following description of some exampleimplementations and corresponding results. Some experimental data ispresented herein for purposes of illustration and should not beconstrued as limiting the scope of the disclosed technology in any wayor excluding any alternative or additional embodiments.

A first example of certain implementations of the disclosed technologyand corresponding results will now be described with respect to FIG. 9 ,in which a graphical depiction is provided showing results from a finiteelement simulation (COMSOL) performed to compare the performance of aPCB based catheter tip utilizing the inter-connected metal layers with acatheter tip without such the inventive components (hereafter “standardflex circuit). The simulation parameters were approximately identicalfor the standard flex circuit and dual metal layered examples, regardingboth the ablation conditions (e.g., time, ablation current, irrigation,position of the ablation catheter, etc.) and the environment comprisingblood and tissue with the relevant thermoelectric properties andgeometry. The ablation catheter 22 of the example analysis was set at a45° angle to the tissue, with penetration depth of 0.8 mm, which wereconsidered typical and normal working conditions. Two scenarios wereanalyzed, including a first scenario where the ablation current was setat 0 about 0.63 Amperes for up to 30 s, equivalent to 30-40 W dependingon measured impedance. Results of this first scenario are shown in FIGS.9 and 10 . A second scenario included the ablation current being set at0.9 A for up to 5 s, equivalent to 80-100 W depending on measuredimpedance. Safety in both scenarios was evaluated where temperaturesover 130° C. because such temperatures are considered dangerous with ahigh probability that the tissue will be ruptured by steam build-up(e.g., steam-pop).

Turning to FIG. 9 which shows results of the first scenario, atemperature field is depicted at approximately 130° C. maximum with astandard flex circuit distal tip. In particular, it can be seen thatdistal tip 32 has been positioned on an ablation surface and maintainedfor approximately 4.7 seconds with ablation current about 0.63 Amperesthereby resulting in a lesion width of approximately 4.6 mm and a lesiondepth of approximately 3.0 mm. FIG. 10 depicts a temperature field atapproximately 130° C. maximum for an example dual metal layered distaltipped ablation catheter. In particular, it can be seen that distal tip32 has been positioned on an ablation surface and maintained for 30seconds with ablation current about 0.63 Amperes thereby resulting in alesion width of approximately 8.9 mm and a lesion depth of approximately5.6 mm. In other words, when compared with the depicted results of thestandard flex circuit distal tip, the dual metal layered distal tip(e.g., similar embodiment of tip 32 illustrated in FIGS. 7-8 ) atablation current about 0.63 Amperes demonstrated approximately about93.5% improvement in lesion width (i.e. from approximately 4.6 mm toapproximately 9.6 mm), approximately about 86.7% improvement in lesiondepth (i.e. 3 mm to 5.6 mm), and approximately about a 538.3% percentimprovement in what is believed to be a clinically safe ablation time(i.e. the ablation time between observations of unsafe temperatures fromabout 4.7 secs. to about 30 secs). Stated differently, the catheter tip32 construction of FIGS. 7-8 was demonstrably safer and more effective,longer-lasting, and imparted a larger ablation zone than standard flexcircuit tips at ablation current about 0.63 Amperes.

Turning to FIG. 11 which shows results of the second scenario, atemperature field is depicted at approximately 130° C. maximum with astandard flex circuit distal tip. In particular, it can be seen thatdistal tip 32 of catheter 22 has been positioned on an ablation surfaceand maintained for 1.7 seconds with ablation current about 0.90 Amperesthereby resulting in a lesion width of 4.3 mm and a lesion depth of 2.6mm. FIG. 12 depicts a temperature field at approximately 130° C. maximumfor an examplary dual metal layered distal tipped ablation catheter. Inparticular, it can be seen that distal tip 32 has been positioned on anablation surface and maintained for 4.5 seconds with ablation currentabout 0.90 Amperes thereby resulting in a lesion width of about 6.9 mmand a lesion depth of about 3.6 mm. In other words, when compared withthe depicted results of FIG. 11 the double metal layer (e.g., similarembodiment of tip 32 illustrated in FIGS. 7-8 ), at ablation currentabout 0.90 Amperes the double metal layer example tip demonstratedapproximately about 60.5% improvement in lesion width (i.e. from 4.3 mmto 6.9 mm), approximately about 38.5% improvement in lesion depth (i.e.2.6 mm to 3.6 mm), and approximately about a 164.7% percent improvementin what is believed to be clinically safe ablation time (i.e. ablationtime between observations of unsafe temperatures from about 1.7 s toabout 4.5 s). Stated differently, the catheter tip 32 construction ofFIGS. 7-8 demonstrate what is believed to be a safer and more effective,longer-lasting, and imparted a larger ablation zone than standard flexcircuit tips at ablation current of about 0.90 Amperes.

FIG. 13 depicts a heat flux map with dual metal layers and constructedwith platinum and connected by thermal vias 80 through an example PCB160, whereby catheter 22 during the simulation was positioned atapproximately a 45° angle to the tissue and maintained for 30 seconds at1 mm insertion.

FIG. 14 depicts a temperature map with dual metal layers and constructedwith platinum and connected by thermal vias 80 through an example PCB160, whereby catheter 22 was positioned at a vertical insertion (e.g.,approximately 90° angle with the tissue) and maintained for 2.5 seconds.

FIG. 15 depicts a graph summarizing maximum temperature in the tissueduring ablation as between standard flex circuit and dual metal layereddistal catheter tips 32. The ablation current 0 about 0.63 Amperes (˜35W) is shown across 0-30 s of ablation duration time with temperatureranging from approximately 40-220° C. during ablation. It can be seenthat the temperature curve for the standard flex circuit distal tipreaches the temperature safety limit of 130° C. after approximatelyabout 5 seconds of ablation time. In contrast, the dual metal layereddistal catheter tip of this disclosure never quite reaches thetemperature safety limit of 130° even after 30 seconds of ablation time.

FIG. 16 depicts a graph summarizing maximum temperature in the tissueduring ablation as between flex and double metal layered distal cathetertips 32. The ablation current 0.9 A (˜90 W equivalent) is shown across0-5 s of ablation with temperature ranging from approximately 40-245° C.during ablation. It can be seen that the temperature curve for thestandard flex circuit distal tip reaches the temperature safety limit of130° after approximately about 4.5 seconds of ablation time. Incontrast, the dual metal layered distal catheter tip of this disclosurereaches the temperature safety limit of 130° C. after approximatelyabout 1.7 seconds of ablation time.

FIG. 17 depicts a perspective view of heat generated in a hemisphere ofapproximately 2 mm radius under an example illustration of the dualmetal layered distal tip 32 of the catheter 22 of this disclosure atapproximately about 1.5 W. The depicted hemisphere is approximatelyabout where the ablation center of distal tip 32 generally resides. Ofcourse, the depicted hemisphere is merely representational of oneembodiment and other shaped ablation zones are contemplated as well asablation radii according to the solution of this disclosure.

FIG. 18 depicts a perspective view of an example embodiment of the dualmetal layered distal tip of the catheter in contact with tissue. Totalheat flux through the surface of the distal tip 32 in FIG. 18 isapproximately about −0.82 W whereas it is approximately about −0.3 W fora standard flex circuit tip of this disclosure. Thus, out of theoriginal 1.5 W there remains 0.7 W in the dual metal layered distal tipvs 1.2 W in the standard flex circuit case, which is approximately a71.5% increase. Other cases (e.g. single metal layer) were shown to fallin between the extremes. While the foregoing oversimplifies the variousfeatures and systems, it is relatively clear that without an efficientmethod of cooling at the hotter region of the distal tip 32, theablation zone will develop temperatures high enough to preclude theformation of a lesion beyond a certain size within the limits of safety.

FIG. 19 is a flow diagram for a method 1900 in accordance with someembodiments of the present disclosure. Step 1910 includes inserting,into a body of a subject, a distal end of a catheter, the distal endcomprising an outer layer of a thermally-conducting metal; an innerlayer of an thermally-conducting metal; a polymer layer between theinner and outer layer; and a plurality of thermal bridges selectivelypositioned between the inner and outer layers and through the polymerlayer thereby significantly increasing the heat transfer of the cathetertip through the polymer layer. Step 1920 includes while contacting thetissue, passing an ablation current, via the outer layer, into thetissue, such that heat is generated in the tissue and is transferred,via the thermal bridges, to the inner thermally-conducting layer. Step1930 includes subsequently to inserting the distal end of the catheterinto the body of the subject, contacting tissue of the subject with theouter layer. Step 1940 includes evacuating the heat, from the innerthermally-conducting layer, into blood of the subject, by passing anirrigating fluid through a plurality of irrigation channels through theinner layer, the outer layer, and the polymer layer.

FIG. 20 is a flow diagram for a method 2000 of manufacturing a cathetertip electrode, in accordance with some embodiments of the presentdisclosure. Step 2010 includes drilling a plurality of thermal bridges,through a flexible thermally-insulating polymer substrate. Step 2020includes using a thermally-conducting metal to sandwich the flexiblethermally-insulating polymer substrate between an inner surface and anouter surface. It is understood that any thermally conductive materialcan be used in the herein disclosed examples, including diamond. Thecatheter tip electrode can also be a separate thin (e.g., approximatelyabout 1 micron) metal layer deposited over the thermally conductinglayer.

Alternatively or additionally to the traces described above, any othersuitable electric or electronic components may be deposited onto theinner surface of the substrate. Such components may include thermistorsfor measuring the temperature of the tissue, pressure sensors formeasuring the pressure applied to the distal end of the catheter, and/orelectromagnetic sensors for navigating the catheter. These components(along with suitable surrounding exclusion zones) may be masked orcovered whenever such masking or covering is required, as describedabove for the traces.

It is noted that the scope of the present disclosure includes anysuitable modification to method 82 with respect to the order of thesteps that are performed and/or with respect to the various materialsthat are used, as will be apparent to any person of skill in the art.For example, any suitable thermally-conducting metal may be used in lieuof copper, gold, or constantan.

In general, the embodiments described herein may be combined with any ofthe embodiments described in US Patent Application Publication2018/0110562 or U.S. patent application Ser. No. 15/793,126, whoserespective disclosures are incorporated herein by reference.

It will be appreciated by persons skilled in the art that the presentdisclosure is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of embodiments of the presentdisclosure includes both combinations and subcombinations of the variousfeatures described hereinabove, as well as variations and modificationsthereof that are not in the prior art, which would occur to personsskilled in the art upon reading the foregoing description. Documentsincorporated by reference in the present patent application are to beconsidered an integral part of the application except that to the extentany terms are defined in these incorporated documents in a manner thatconflicts with the definitions made explicitly or implicitly in thepresent specification, only the definitions in the present specificationshould be considered.

What is claimed is:
 1. An electrophysiology catheter tip for use inablation, the catheter tip comprising: a polymer layer comprising aninner surface and an outer surface, and shaped to define (i) multiplenarrower channels passing between the inner surface and the outersurface, and (ii) one or more wider channels passing between the innersurface and the outer surface; an outer layer of an electrically andthermally conducting metal covering at least part of the outer surface;an inner layer of an electrically and thermally conducting metalcovering at least part of the inner surface; a plating layer of theelectrically and thermally conducting metal that plates the widerchannels to connect the outer layer to the inner layer; and respectivecolumns of the electrically and thermally conducting metal that fill thenarrower channels to connect the outer layer to the inner layer, theouter layer comprising a conductive path on the outer surface betweenand joining the columns, and the inner layer comprising a conductivepath on the inner surface between and joining the columns.
 2. Thecatheter tip according to claim 1, wherein the polymer layer is shapedto define at least 1000 of the multiple narrower channels.
 3. Thecatheter tip according to claim 1, wherein the narrower channels and thewider channels electrically and thermally join the inner and outerlayers, thereby permitting heat transfer from an outside to an inside ofthe catheter tip and temperatures are coolable by saline used duringirrigation.
 4. The catheter tip according to claim 1, wherein the one ormore wider channels allow irrigation liquid to transfer heat to theouter surface; and wherein a diameter of each of the multiple narrowerchannels is approximately about 60 microns.
 5. The catheter tipaccording to claim 1, wherein distance between the narrower channels isapproximately about 0.2 to 0.3 mm.
 6. The catheter tip according toclaim 1, further comprising: a plurality of electrodes oriented tocontact cardiac tissue; and the one or more wider channels comprise oneor more metal irrigation holes disposed between the inner and outerlayers.
 7. The catheter tip according to claim 6, wherein a thickness ofwall plating in the irrigation holes is approximately about 25 microns.8. The catheter tip according to claim 6, wherein the outer layercomprises a total shell thickness approximately about 130 microns. 9.The catheter tip according to claim 6, wherein the catheter tip isconfigured to generate a heat generated hemispherical ablation zone ofat least approximately 2 mm radius.
 10. The catheter tip according toclaim 6, further comprising: a cylindrical section; and a dome sectiondistal of the cylindrical section, wherein the multiple narrowerchannels and the one or more wider channels are thermal bridgespositioned in the cylindrical and dome sections.
 11. The catheter tipaccording to claim 1, further comprising a catheter configured forinsertion into a body of a subject, wherein a supporting structure iscoupled to a distal end of the catheter, and wherein the distal end ofthe catheter comprises a flow diverter configured to divert fluidreceived from a proximal end of the catheter, and wherein the supportingstructure is coupled to the flow diverter such that the flow diverter isdisposed inside of an interior lumen.
 12. The catheter tip according toclaim 1, wherein the multiple narrower channels comprise openings at theouter surface that comprise at least ten percent of a total surface areaof the outer surface.
 13. The catheter tip according to claim 1, whereinthe wider channels and the narrower channels increase heat transfer ofthe catheter tip through the polymer layer such that when approximately0.63 Amperes are delivered to the outer layer, at least approximately100% improvement in clinically safe ablation time is achieved ascompared to a standard flex circuit ablation catheter with approximately0.63 Amperes and when approximately 0.90 Amperes are delivered to theouter layer of the tip, at least approximately 100% improvement inclinically safe ablation time versus a standard flex circuit ablationcatheter with ablation current of about 0.90 Amperes.